Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing our new design.

The outermost broken line shows an environment, whereas the remaining broken lines show a display screen and elements of a graphical user interface. None of the broken lines form part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a graphical user interface, substantially as shown and described. 